Update the about page

[edwardchalstrey1]

Requested enahancement or feature

The "What is Gambit?" section from the docs site has been moved to here: https://www.gambit-project.org/about/

The following changes should be made:

• Update content/about.md to accurately represent the present state of the project
• Update the history section (or move to it's own separate page) so that scrolling down you get sections ordered by decade, with the key highlights, similar to the timeline idea (Add "Through the years" timeline #17) but without the graphic and more information
• Once ready, add /about to the navbar